Quine and Davidson adopt a third-person perspective not just on meaning, but also on the mind. Mental phenomena must be manifestable, at least in principle. The manifestability of the mental has a distinguished pedigree in the pragmatists, Wittgenstein and Ryle. But it is stronger and more controversial than the manifestability of meaning. Like our two protagonists, I shall concentrate on what Davidson calls ‘thought’ (SIO 98–9). By this he means all the propositional attitudes, but this generic term is less misleading, since neither Quine nor Davidson regards beliefs, desires, etc. as attitudes towards propositions.

In Quine, there are three lines of reasoning to support the manifestability of the mental. The first two are connected to his naturalistic preoccupation with science. Naturalized epistemology elucidates the relation between theory and evidence through a scientific account of the relation between theoretical talk and observational talk. It can do so, because both scientific theories and scientific observations must be capable of being expressed in words (WO 26; OR 89; RR 34–9; NNK 74–5). This claim seems incontestable. Even if there are ineffable truths and observations that cannot be expressed in language, such as the ineffable insights and experiences alleged by mystics, they will not qualify as scientific, since science is a cooperative attempt to establish the nature of reality.

Furthermore, the requirement of manifestability carries over to non-scientific thoughts, in so far as they are studied by science. The proper perspective for psychology is methodological behaviourism.